The present invention relates to apparatus and methods for manufacturing nonwoven webs and laminates from filaments of one or more thermoplastic polymers.
Melt spinning technologies are routinely employed to fabricate nonwoven webs and multilayer laminates or composites, which are manufactured into various consumer and industrial products, such as cover stock materials for single-use or short-life absorbent products, disposable protective apparel, fluid filtration media, and durables including bedding and carpeting. Melt spinning technologies, including spunbonding processes and meltblowing processes, form nonwoven webs and composites from one or more layers of intertwined filaments or fibers, which are composed of one or more thermoplastic polymers. Fibers formed by spunbonding processes are generally coarser and stiffer than meltblown fibers and, as a result, spunbonded webs are generally stronger but less flexible than meltblown webs.
A meltblowing process generally involves extruding a row of fine diameter, semi-solid filaments of one or more thermoplastic polymers from a meltblowing die of a melt spinning apparatus and attenuating the extruded filaments while airborne with high velocity, heated process air immediately upon discharge from the melt spinning apparatus. The process air may be discharged as continuous, converging sheets or curtains on opposite sides of the discharged filaments or as individual streams or jets associated with the filament discharge outlets. The attenuated filaments are then quenched with a flow of a relatively cool process air and blown in a filament/air mixture for depositing in a forming zone to form a meltblown nonwoven web on a collector, such as a substrate, a belt or another suitable carrier, moving in a machine direction.
A spunbonding process generally involves extruding multiple rows of fine diameter, semi-solid filaments of one or more thermoplastic polymers from an extrusion die of a melt spinning apparatus, such as a spinneret or spinpack. A voluminous flow of relatively cool process air is directed at the stream of extruded filaments to quench the molten thermoplastic polymer. A high-velocity flow of relatively cool process air is then used to attenuate or draw the filaments to a specified diameter and to orient them on a molecular scale. The process air is heated significantly by thermal energy transferred from the immersed filaments. The attenuated filaments are propelled in a filament/air mixture toward a forming zone to form a nonwoven web or a layer of a laminate on a moving collector.
Spunbonding processes typically incorporate a filament drawing device that provides the high velocity flow of process air for attenuating the filaments. Hydrodynamic drag due to the high velocity air flow accelerates each filament to a linear velocity or spinning speed significantly greater than the speed of extrusion from the extrusion die and applies a tensile force that attenuates the filaments as they travel from the die to the inlet of the filament drawing device. Some additional attenuation occurs between the outlet of the filament drawing device and the collector as the filaments are entrained by the high velocity air exiting the filament drawing device. Conventional filament drawing devices accelerate the filaments to an average linear velocity less than 8000 meters per minute (m/min).
One deficiency of conventional filament drawing devices is that a large volume of high velocity process air is required for attenuating the filaments. In addition, the process air captures or entrains an excessive volume of secondary air from the ambient environment surrounding the airborne filament/air mixture. The volume of entrained secondary air is proportional to the volume and velocity of the process air exiting the filament drawing device. If left unmanaged, such large volumes of high velocity process and secondary air tend to disturb the filaments as they deposit on the collector, which degrades the physical properties of the spunbonded web.
As mentioned above, large volumes of process air are generated during both the meltblowing and spunbonding processes. Moreover, much of the process air is heated and is moving with high velocities, sometimes approaching sonic velocities. Without properly collecting and disposing of the process air and the entrained secondary air, large volumes of high-speed air would likely disturb personnel working around the manufacturing apparatus and other nearby equipment. Further, large volumes of heated process air would likely heat the surrounding area in which the nonwoven web or laminate is being fabricated. Consequently, attention must be paid to collecting and disposing of this process air and entrained secondary air when manufacturing nonwoven webs and laminates with melt spinning technologies.
Management of the process and secondary air is also important with regard to tailoring the characteristics of the filaments as deposited on the moving collector. The homogeneity of the distribution of deposited filaments across the width of the nonwoven web, or in the cross-machine direction, depends greatly on the uniformity of the air flow in the cross-machine direction around the filaments as they are deposited onto the collector belt. If distribution of air flow velocities in the cross-machine direction is not uniform, the filaments will not be deposited onto the collector uniformly, yielding a nonwoven web that is nonhomogeneous in the cross-machine direction. Thus, the variation of the air flow velocity in the cross-machine should be minimized in order to produce a nonwoven web having homogenous physical properties, such as density, basis weight, wettability, and fluid permeability, in the cross-machine direction. Moreover, large volumes of unmanaged air may also affect fiber formation upstream and downstream of the forming zone in the upstream and downstream fiber-making beams, respectively. Therefore, effective and efficient disposal of large volumes of air is necessary to avert irregularities in the physical properties of the nonwoven web.
Filaments deposited onto the collector have an average fiber orientation in the machine direction (MD) and an average fiber orientation in the orthogonal cross-machine direction (CD). The ratio of filament orientation, termed the MD/CD laydown ratio, indicates the isotropicity of the nonwoven web and strongly influences various properties of the nonwoven web, including the directionality of the tensile strength or flexibility of the web. Given a uniform distribution of air flow velocities in the cross-machine direction, the distribution of air flow velocities in the machine direction controls the MD/CD laydown ratio and, therefore, is an important consideration in the management of the large volumes of process and secondary air.
Various conventional air management systems have been used to collect and dispose of the flow of process and secondary air generated by melt spinning apparatus. Most conventional air management systems include an air moving device, such as a blower or vacuum pump, and a collecting duct having an intake opening positioned below the collector proximate to the forming zone for collecting the air and an exhaust opening coupled in fluid communication with the air moving device for disposing of the collected air. In some of these conventional systems, the negative pressure applied at the intake opening is controlled by one or more movable dampers positioned at the threshold of the intake opening. In other conventional air management systems, the collecting duct is subdivided into an array of smaller air passageways in which each individual air passageway includes an intake opening, an exhaust opening, and an air moving device coupled in fluid communication with the exhaust opening for drawing the collected air into the individual intake openings. Control of the negative air pressure applied at the intake opening is provided by multiple moveable dampers each associated with an exhaust opening of one of the air passageways.
Controlling the distribution of air flow velocities proximate to the forming zone in both the cross-machine and machine directions simultaneously, however, has proven challenging for conventional air management systems. Conventional air management systems, such as those described above, are incapable of systematically controlling the directionality or symmetry of the air flow velocities in the machine direction while maintaining a relatively uniform distribution of air flow velocities in the cross-machine direction. In particular, movable dampers in such conventional systems either are incapable of varying the distribution of air flow velocities in the machine direction or cannot vary the distribution of air flow velocities in the machine direction without significantly reducing the uniformity of the air flow velocities in the cross-machine direction. As a result, conventional air management systems lack the ability to select the distribution of air flow velocities in the machine direction in order to effectively control the MD/CD laydown ratio. It follows those melt spinning processes using such conventional air management systems cannot control or otherwise tailor the properties of the nonwoven web in the machine direction.
What is needed, therefore, is an air management system for a melt spinning system that can manipulate the disposal of the process air so as to control the distribution of air flow velocities near the forming zone for the nonwoven web in the machine direction and maintain a uniform air flow in the cross-machine direction. Also needed is a melt spinning system capable of generating reduced volumes of process air and entrained secondary air for disposal.
The present invention provides a melt spinning system and, more particularly, a melt spinning and air management system that overcomes the drawbacks and disadvantages of prior melt spinning and air management systems. The air management system of the invention includes at least one air handler for collecting air discharged from a melt spinning apparatus. The air handler generally includes an outer housing having first walls defining a first interior space and an inner housing positioned within the first interior space and having second walls defining a second interior space. One of the first walls of the outer housing has an intake opening positioned below a collector for admitting the discharged air from a melt spinning assembly into the first interior space and another of the first walls of the outer housing has an exhaust opening for exhausting the discharged air. The second interior space is coupled in fluid communication with the exhaust opening and one of the second walls of the inner housing has an elongate slot with a major dimension in a cross-machine direction and coupling the first interior space in fluid communication with the second interior space.
In certain embodiments of the invention, an adjustable flow control device is positioned in the first interior space of the air management system. The flow control device is operative for controlling the flow of discharged air between the first interior space and the second interior space.
In other embodiments of the invention, an air-directing member is positioned outside of the first interior space of the air management system and proximate to the intake opening. The air-directing member extends in the cross-machine direction and divides the intake opening into first and second portions in the machine direction.
According to the principles of the invention, an apparatus is provided which includes a melt spinning apparatus and an air management system having three air handlers. The melt spinning apparatus is operative to extrude filaments of material and is positioned vertically above a collector. A first air handler of the air management system is positioned directly below the melt spinning apparatus in a forming zone. A second air handler is positioned upstream of the first air handler and the forming zone. A third air handler is positioned downstream of the first air handler and the forming zone. The second and third air handlers each include an air-directing member, as described above, and an adjustable flow control device, also as described above.
According to the principles of the present invention, an apparatus is provided that is configured to discharge filaments of material onto a moving collector. The apparatus includes a melt spinning apparatus operative for extruding filaments, a filament drawing device positioned between the melt spinning apparatus and the collector, and an air handler having an intake opening positioned proximate to the collector. The filament drawing device has an inlet for receiving the filaments from the melt spinning apparatus and an outlet for discharging the filaments toward the collector. The filament drawing device is operative for providing a flow of process air sufficient to attenuate the filaments of material. The flow of process air entrains secondary air from the ambient environment between the outlet and the collector. The intake opening of the air handler collects process air discharged from the filament drawing device and secondary air entrained by the process air. The apparatus further includes a forming chamber having a side wall at least partially surrounding the intake opening of the air handler and the outlet of the filament drawing device, an entrance opening upstream of the intake opening, and an exit opening downstream of the intake opening. The side wall defines a process space for the passage of the filaments of material from the outlet of the filament drawing device to the collector and partitions the process space from the surrounding ambient environment. The entrance and exit openings are dimensioned so that at least the collector can traverse the process space. The side wall of the forming chamber includes a perforated metering sheet configured to regulate the flow of air from the ambient environment into the process space.
The invention further provides a method for depositing a nonwoven web of filaments on a collector moving in a machine direction in which filaments of material are discharged from a melt spinning assembly discharging filaments of material from a melt spinning assembly and mixed with a flow of process air. The filaments of material are deposited on the collector and the process air is collected with an intake opening of an air management system having a substantially uniform collection of the discharge air in the cross-machine direction and a selectively variable ratio of air flow velocity in the machine direction to air flow velocity in the cross-machine direction.
Various additional advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description taken in conjunction with the accompanying drawings.